1. Field of the Invention
This invention relates to a fluid clutch provided with a function of automatically controlling the operation of a cooling fan applied mainly to an internal combustion engine of a vehicle in response to an ambient temperature condition.
2. Description of the Prior Arts
As a fluid clutch for controlling the rotation of a cooling fan of an internal combustion engine of a vehicle, a type of fluid clutch which transmits a driving torque of a driving disc to a case by oil supplied to a torque transmitting chamber has been typically used. As the structure of such a fluid clutch, for example, a constitution of a coupling device (fluid clutch) where the inside of a sealed case is divided into the torque transmitting chamber and an oil reserving chamber by means of a partition plate, the driving disc which is driven by a driving part is rotatably disposed in the inside of the torque transmitting chamber, oil in the oil reserving chamber is supplied to the torque transmitting chamber through a flow-out adjusting hole formed in the partition plate, and oil in the torque transmitting chamber is returned to the oil reserving chamber through a circulation passage has been known (see Japanese publication SHO 63-21048). In this type of fluid clutch, the driving torque of the driving disc is transmitted to the sealed case by oil supplied to the torque transmitting chamber from the oil reserving chamber, a fan mounted on the sealed case is rotated so that the cooling of an engine of a automobile is performed, for example. Furthermore, in this type of fluid clutch, an ambient temperature is detected by a bimetal and in response to the elevation of the detected temperature, the degree of opening of the flow-out adjusting hole is increased. Accordingly, an amount of oil in the inside of the torque transmitting chamber is increased so that the rotational speed of the sealed case is increased and the fan is rotated at a high speed thus enhancing the cooling effect.
This type of fluid clutch, however, has following problems.
That is, under the condition that a large amount of oil is present or filled in the inside of the torque transmitting chamber, at the time of restarting the engine or at the time of rapid acceleration during the operation, following the acceleration of the driving disc of the driving side, the rotation of the case of the driven side (cooling fan) is also rapidly increased due to a large amount of oil present in the inside of the torque transmitting chamber, although for a short time. This phenomenon is generally called `a drag phenomenon` or `an attendingly rotating phenomenon` and gives rises to a noise of fan and an accompanying discomfort and deteriorates the fuel expense.
`The drag phenomenon` of the conventional fluid clutch which occurs at the time of restarting the engine becomes more apparent corresponding to the increase of an amount of oil in the inside of the torque transmitting chamber. As means for solving this problem, for example, Japanese publication SHO 63-21048 proposes means where oil flowed out through the flow-out adjusting hole of the partition plate is first introduced to the opposite side in the diametral direction and then is supplied to the inside of the torque transmitting chamber.
With such a structure, under the condition that substantially no oil is present in the torque transmitting chamber and a large amount of oil is present in the oil reserving chamber, even when the engine is stopped, the inflow of oil from the oil reserving chamber to the torque transmitting chamber can be prevented and hence, no `drag phenomenon` occurs at the time of restarting the engine. However, under the condition that a large amount of oil is present in the inside of the torque transmitting chamber, the structure is not effective for the prevention of `the drag phenomenon` at the time of restarting after the engine is stopped and at the time of rapid acceleration during the operation.